Apparatuses that amplify by selecting one out of multiple signals have traditionally been constituted by combining switches for selecting the signal path with amplifiers for amplifying the signals (for instance, refer to JP (Kokai) 5[1993]-276,045 (page 4, FIG. 1).
The above-mentioned types of apparatuses use a reed relay or other mechanical switch in order to switch signals of a wide band region while controlling distortion. For instance, semiconductor testers that are used to test ICs comprise multiple mechanical switches and operational amplifiers in order to measure multiple signals which are output from an IC with few measurement resources. The number of pins in an IC or device under test increases each year and the band of the signals output from an IC becomes wider each year. Therefore, semiconductor testers must comprise more mechanical switches and operational amplifiers. However, mechanical switches consume a large amount of electricity and have a larger mounting surface area than other individual components and ICs (integrated circuits). Semiconductor testers have a limited housing size and electrical power; therefore, they cannot comprise this many mechanical switches and operational amplifiers. Moreover, semiconductor testers are required to measure signals output from an IC without distortion and they therefore cannot use semiconductor switches for switching signals.
Thus, an object of the present invention is to provide a current feedback-type operational amplifier having a function for amplification by selecting one signal out of multiple input signals.